This application relates to water heaters, and particularly, to devices that improve the heating efficiency of water heaters.
Water heaters having internal electric resistance heating elements are well-known and in common use both domestically and commercially. Conventional designs of this type typically consist of a water tank into which cold water is introduced near its bottom, and water heated by the elements is removed from its top. The heating elements are usually in the form of two metallic sheathed electric resistance heating elements of the Calrod(copyright) type which extend into the tank from its inner sidewall and are fully exposed to the water in the tank.
Circulation of water inside the tank is normally very poor. This causes xe2x80x9clayeringxe2x80x9d or layers of significantly cooler water to develop immediately below each element. The effect of layering on overall heating efficiency is two-fold. First, it impedes heat transfer from the elements to the water in the tank, which affects the heater""s recovery rate in an undesirable manner. Second, to a certain extent, layering reduces the effective hot water holding capacity of the heater.
As a person skilled in the art would know, water heater recovery rate is directly related to a water heater""s capacity to heat an amount of cold water introduced into the tank in response to removal of heated water. In order to overcome this heating inefficiency, I invented a thermosiphon apparatus readily adaptable to conventional water heater designs as shown in my U.S. Pat. No. 4,777,347. However, because the efficiency of water heaters and water heater construction is typically regulated by state standards, many water heater manufacturers were unwilling to modify their tanks in order to implement my thermosiphon apparatus. Therefore, there is a need for a thermosiphon apparatus that improves the efficiency of existing water heaters without involving modifications to the existing water heater tanks by the manufacturers.
The present invention is directed to a thermosiphon apparatus that satisfies this need for improving the efficiency of existing water heaters without involving modifications to the existing water heater tanks by the manufacturers. A thermosiphon apparatus having features of the present invention comprises a water tank, a cold water inlet for delivering cold water to a lower region of the tank, and a hot water outlet for removing heated water from an upper region of the tank. The cold water inlet is substantially immersed in the tank and extends generally from an upper wall of the tank to the lower region of the tank. Two electric heating elements, each immersed in water held in the tank, are positioned between the tank""s upper and lower regions and extend generally horizontally inwardly into the tank from the tank""s inner sidewall.
A tubular sleeve surrounds each heating element. The sleeve includes a first plurality of openings formed along the length of the sleeve above the heating element, and a second plurality of openings formed also along the length of the sleeve, but below the element. The total area of the upper openings exceeds the total area of the lower openings. Water trapped or held inside the sleeve and surrounding the element is quickly heated and the previously described arrangement of sleeve openings generates an upwardly directed flow of heated water.
An external bypass conduit is provided which has an upper end connecting to the cold water inlet, a lower end connecting to the hot water outlet, and a flow control valve inside the bypass conduit that regulates waterflow through the bypass conduit.
The holes or openings in each sleeve, in combination with the bypass conduit, generate a thermosiphon effect. Normally, and as a person skilled in the art would know, heat tends to rise upwardly. This means the upper region of the tank would naturally tend to be warmer than the lower region. However, the thermosiphon effect generated by the apparatus causes a xe2x80x9croll-overxe2x80x9d of heated water from the upper to lower regions. This both eliminates layering in the tank and substantially improves the tank""s recovery rate.
The invention may also be applied to a conventional gas water heater. In this form, an external bypass conduit is provided which has an upper end connecting to the cold water inlet, a lower end connecting to a hot water conduit, and a flow control valve inside the bypass conduit that regulates water flow through the bypass conduit. The hot water conduit can be the hot water outlet conduit or a separate additional conduit. The flow control valve prevents backflow through the bypass conduit when hot water is being drawn from the tank. When no water is being drawn from the tank, the flow control valve opens to allow thermosiphonic circulation from the lower hot water outlet connection to the upper cold water inlet connection without the flow control valve interfering with the thermosiphonic flow.
Operation of the apparatus will be more fully explained in the following description of the best mode for carrying out the invention, when read in conjunction with the accompanying drawings and claims.